Thats my worry, who to? stating what information? I have read other topics but none seem to be the same situation as mine so I worry that I may send wrong details or too much information etc

Hi I've recently cancelled my direct debit to Xercise4less and received a letter from Harlands saying I owe them admin fee of £25 aswell as the monthly fee etc... I had been with the gym for over 3 years now (rolling contract atm). I haven't stepped foot in the gym since 27/06/16. So over £175 wasted (my reason for cancelling). The letter I received from Harlands states that if I do not pay by 10 December I will be charged another £25. So I phoned up Harlands today and offered to pay what I owed (£9.99) without the admin fee ofcourse. But as you'd expect they had declined the offer. I don't know what my next step is to take? I have read a few topics and I'm not 100% sure what to do in my personal situation thanks all.